The difference is that parents have the right and even the obligation to set boundaries for their children to protect them and direct their growth and development.
If I buy a book as a gift for an adult I would be rude to tell that person not to stay up so laye reading it that they can't perform at work. I have a right and even a duty to tell my child they need to stop reading at a certain time so they are awake and focused at school. If I buy a game system for an adult I can't tell them what games they can get to play on it in their own home. I can for my kid and many would say I have an obligation to do so.
If it's a matter of giving the kid a bedtime, that's fine! We were saying 7:30 is weirdly late for his age, not that she doesn't have the right to tell him not to call after any
specified time. If she'd said 9 (a generally accepted "too late to call" cutoff by many people) or 10, who would care?
And whatever your rights and duties concerning your child, do you not also have a responsibility to protect his privacy? If you make these rules about games and books, do you then blast them to the internet with his full name on them? It's the public nature of the lecture (as well as the smugness) that bothers me the most, I think. Making it public makes it a self-aggrandizement for the mother rather than boundaries for the child. Think of that "who is being served?" question that comes up on here sometimes. The person who is being served here is the mother, by getting all those extra hits on her blog.